1. Field of the Invention
The present invention relates in general to an improved crossbow and, more particularly, to a crossbow having improved speed and reduced noise characteristics.
2. Description of the Prior Art
Crossbows have been known for centuries. By allowing the shooter to mechanically retain the bow in the cocked position, the shooter is provided an advantage over a traditional archer who must utilize muscular force to retain the bow in the cocked position. While crossbow design remained substantially unchanged until the twentieth century, crossbow design has been subject to many recent developments which have dramatically increased performance.
One improvement has been the provision of cams on the crossbow to increase the mechanical advantage associated with the draw of the bowstring. One drawback associated with such cams is the requirement that the cams be “synchronized” to prevent lateral travel of the rear of the projectile during launch. While such problems are less dramatic in crossbows than in traditional bows, developments such as the utilization of a single cam arrangement, such as that described in McPherson, U.S. Pat. No. 6,267,108, substantially reduces the problems associated with “synchronization.”
Such crossbows still have several drawbacks. As with crossbows of the past, these newer crossbows still locate the limbs of the bows near the forward most portion of the crossbow rail. This orientation positions the bowstring substantially further back along the rail, drastically decreasing the draw length of the crossbow, simultaneously sacrificing speed, and necessarily increasing the draw weight required to obtain desired performance.
As described in Nishioka, U.S. Pat. No. 4,879,987, it is known to reverse the positioning of the limbs in a crossbow to place the bowstring closer to the end of the rail, thereby increasing draw length and the associated power of the crossbow. However, although such devices provide for an increased draw length, by drawing the bowstring from the rear of the cams located on the limbs, the draw length is still not effectively maximized. Additionally, utilizing brackets to locate the cams inward and short of the ends of the limbs, further decreases the potential power of such devices. Still another drawback with such devices is the inclusion of additional cams located on the frame, which increases cost, weight and maintenance of such devices, as well as adding additional friction to further diminish the potential power of the crossbow.
As shown in Nizov, U.S. Pat. No. 5,630,405, it is known in the art to position the cams closer to the ends of the limbs to further increase the power of the crossbow. Such devices also have drawbacks, however, including the pulling of the bowstring from the rear of the cams, which reduces the draw length of the crossbow. Additionally, Nizov fails to position the bowstring at the end of the rail, thereby sacrificing overall draw length and power. Nizov also requires that the majority of the projectile be positioned behind the cocked position of the bowstring. Such an orientation increases the required length of the rail, while failing to provide any concomitant increase in draw length. It would be desirable to increase the utilization of the rail to increase power and reduce the weight and bulkiness of the crossbow.
As described in Nishioka, U.S. Pat. No. 4,766,874, it is known in the art to provide a crossbow with the above described reverse limb orientation to increase draw length, and to further draw the bowstring from the forward portion of the cams to additionally increase draw length, and the associated power stroke. One drawback associated with such devices, however, is the decrease in draw length associated with providing brackets which locate the limb cams rearwardly and inwardly of the limbs. An additional drawback is that such devices locate the bowstring substantially rearward of the end of the crossbow rail, substantially reducing the draw length and power stroke. It would be possible to increase the powerstroke associated with prior art crossbows by increasing the axle-to-axle distance associated with the axles journaling the limb cams to the limbs. Larger axle-to-axle distances, however, are undesirable, especially in hunting and/or tree stand applications where the increased size and weight associated with the increased axle-to-axle distance would make hunting more difficult. It would, therefore, be desirable to minimize the ratio of the axle-to-axle distance to the powerstroke.
Still another drawback associated with such devices is the inclusion of pulleys located below the rail of the crossbow. This additional feature increases the weight, cost and maintenance of such devices, while adding additional friction, further decreasing the potential speed of the crossbow. It would be advantageous to eliminate these additional frictional elements and to increase the power stroke to exploit the full length of the rail in imparting power to the projectile.
As noted above, while there have been several advancements in the field of crossbows, the existing prior art evidences numerous drawbacks, including the failure to utilize the entire potential power stroke of both the forward and rearward ends of the rail, undesirable location of pulleys and cams, and the inclusion of additional frictional parts, further robbing the crossbow projectile of additional speed. The difficulties encountered in the prior art discussed hereinabove are substantially eliminated by the present invention.